In her recent book of essays, Negotiating with the Dead, Margaret Atwood analyses the unique power of the fictional terrain where voice is still heard beyond death. Using Alice Through the Looking Glass as one of her analogies, she says: "The act of writing takes place at the moment when Alice passes through the mirror. At this one instant... Alice is neither here nor there, neither art nor life, neither the one thing nor the other, though at the same time she is all of these at once. At that moment time itself stops, and also stretches out, and both writer and reader have all the time not in the world."

The dead 14-year-old heroine of Alice Sebold's The Lovely Bones is stranded in a much less supple, much more primitive and chronological parenthesis. This novel, Sebold's first, was clearly born from her own horrific rape experience as a teenager, detailed in her memoir Lucky (1999), whose first paragraph reads: "In the tunnel where I was raped... a girl had been murdered and dismembered. I was told this story by the police. In comparison, they said, I was lucky." The Lovely Bones, with its posthumous narrator telling the story of her brutal rape and murder and their aftermath, has been a massive seller in the US, garnering comparisons with Harper Lee's To Kill a Mockingbird.

"My name was Salmon, like the fish, first name Susie," it disarmingly begins. "I was 14 when I was murdered on December 6, 1973.. . It was still back when people believed things like that didn't happen." Susie Salmon, whose bones are shut in an old safe and sunk in quicksand by her neighbour Mr Harvey, spends the book watching and narrating, from her perfect adolescent heaven, the tale of her loss and the rupture her murder brings about in the lives of her family, her killer and her friends. They are characters from an above-average TV movie inhabiting this new "ground zero" - the sharp-witted sister, the distracted mother, the too-hurt father, the ethnic boy, the life-is-tough adolescent girl, the oddball murderer, the tipsy too-ebullient grandmother and the crumpled, touched-by-tragedy detective.

Not much is possible from heaven, though Susie makes occasional contact with those she misses. Time inevitably passes ("however haphazardly, everyone I'd known was growing up"), bringing its own patterns of healing and meaning. The book's "bones", above all, cease to be those of Susie's never-found body, or the animal bones her creepy killer plays with to distract himself from other young girls; instead they become "lovely", being connections between loved ones "that happened after I was gone. And I began to see things in a way that let me hold the world without me in it."

Perhaps the reason The Lovely Bones has been such a hit in the US is something to do with the aftermath of public mourning after last year's terrorism, the reassurance and satisfaction of being able to hear the voice of the gone and to piece together the future after cataclysm. I can't think why else, because though it's a great idea for a book, and though its opening chapters are shattering and dazzling in their mix of horror and normality, after the first 50 pages the energy dissipates and something much blander than the opening has promised starts happening both in the writing and in the narrative. Possibly this is an interesting, calculated blandness, Sebold being concerned with the creation of a safe and supportive place in the face of a horror she herself has been so close to. Regardless, it deadens the narrative.

In place of the multiple perspective, the kick-ass attitude of voice and the dismissal of the mawkish that we began with, the novel becomes a hybrid of realism and wishful thinking. This is Susie's response from heaven to her sister's first kiss, a couple of weeks after her own rape and murder: "He put his hand on her forearm and - Wow! - what I felt when he did that. Lindsey had a cute boy in the kitchen, vampire or no! This was news, this was a bulletin - I was suddenly privy to everything. She never would have told me any of this stuff."

The Lovely Bones is a determined reiteration of innocence, a teeth-gritted celebration of something not dismembered or shattered at all, but continuous: the notion of the American family unit, dysfunctional, yes, but pure and good nonetheless. It's a celebration that is hard-won, often vivid, sometimes moving, comic and sweet, but that has to be treated with at least a little unease when you consider how the narrative presents us with its villain, the outsider, who is identified by Susie's family by instinct after they simply perceive the man to be a little odd, and after odd, malevolent. "Why, my father wondered, did people trust the police so much? Why not trust instinct? It was Mr Harvey and he knew it." We do too, because Susie told us so on page six - and this easy fait accompli of knowing who's bad and who's good is hardly comparable to Lee's To Kill a Mockingbird, a book that redefined the word "liberal" and challenged all the small-town instincts about right and wrong.

At the heart of The Lovely Bones is an unwritten book about loneliness and the ways in which a too-perfect world is stifling. Though it has its very fine moments, Sebold's novel misses the moral complexity and compellingness of Lucky, which dealt with its dysfunctions, addictions, helpless blindnesses and hypocrisies with a raw honesty, containing bladedly ambiguous sentences like: "I knew now that I had been raped I should try to look good for my parents."

Perhaps it is inevitable that Sebold simplifies in this way, dealing with the kind of subject matter which, even without a September 11 to heighten people's sensitivities and paranoia, caused a furore of anger and calls for censorship in the US when AM Homes published her truly classic fictional analysis of child murder, innocence, American norms and perceived insiders and outsiders, The End of Alice, six years ago. The End of Alice was itself a critical examination of the uses and acceptabilities of blandness - a dialogue between a bombastically voiced elderly male convict and his apparent opposite, a bland-talking straight-A college girl, both revealed by Homes to be equally horrifying paedophiles. But now clearly isn't the time for anything so discomforting. The Lovely Bones is so keen in the end to comfort us and make safe its world that, however well-meaning, it avoids its own ramifications.